Microstructure And Properties Of High-entropy Alloy Cladding Layer Remanufactured By Micro-beam Plasma Additives

In this study,for the purpose of intensive materials and remanufacturing,the CoCrFeMnNi high-entropy alloy cladding layer was prepared on the Q235 substrate by micro-beam plasma additive remanufacturing.The effects of heat treatment and Al element on the microstructure,wear resistance,corrosion resistance and high temperature oxidation resistance of CoCrFeMnNi high entropy alloy cladding layer were systematically investigated.In view of the influence of the medium temperature precipitation in CoCrFeMnNi on the microstructure and properties of the cladding layer,the effects of heat treatment at 500℃,700℃,900℃and 1160℃for 4 h on the microstructure and properties of cladding layers by micro-beam plasma additive remanufacturing were studied.The remanufactured cladding layers had a small dilution rate and no obvious macro defects.The CoCrFeMnNi high-entropy alloy cladding layer was a single FCC phase,and the microstructure was a dendritic structure.After heat treatment at 500℃,a small amount of Cr-rich BCC phase precipitated at the grain boundary of the cladding layer.However,after heat treatment at 700℃,the Cr-richδphase precipitated at the grain boundary of the cladding layer.Due to the presence of the precipitated phases,the average microhardness of the cladding layer increased from 158.9HV0.2 to 181.0HV0.2,and wear resistance of the cladding layer increased first and then decreased as the heat treatment temperature increased.The CoCrFeMnNi cladding layer had a large amount of corrosion-resistant elements such as Cr and Ni,and its corrosion resistance was superior to that of 304 stainless steel.The tafel curve showed that the heat treatment reduced the corrosion resistance of the alloy cladding layer in 3.5%Na Cl solution to some extent.The cladding layers were heat-treated at 900℃for 100 h for high temperature oxidation,and the diffusion of metal atoms such as Mn controlled the entire oxidation process.As the heat treatment temperature increased,pore layer and grain boundaries were more conducive to atomic diffusion,and the Mn atoms diffused to the surface to form an intimate oxide film,which reduced the high temperature oxidation resistance of the cladding layer.Based on the low microhardness,wear resistance and high temperature oxidation resistance of the CoCrFeMnNi alloy cladding layer,the effect of Al element on the microstructure and properties of Al_xCoCrFeMnNi（x=0,0.5,1.0,1.5 and 2.0）high-entropy alloy cladding layers was investigated.The results showed that the microstructure of Al_xCoCrFeMnNi high-entropy alloy cladding layer was dendritic structure.As the Al content increased,the FCC phase in the cladding layer decreased,the Al/Ni-rich BCC phase increased,and the average microhardness and wear resistance of the cladding layer increased.When x=1.0,the average microhardness of the cladding layer reached 556.5HV0.2.In the 3.5%Na Cl solution,the Al_xCoCrFeMnNi cladding layer formed a myriad of tiny primary cells between the Al/Ni-rich BCC and the FCC phase,and the BCC phase became the corrosion starting point,which reduced the corrosion resistance of the cladding layer.Under high temperature oxidation at 900℃,with the increase of Al content,a fine and dense Al₂O₃oxide film was formed at the bottom of the oxide film of the cladding layer,which slowed down the diffusion of matrix metal atoms and oxygen atoms,and improved the high temperature oxidation resistance of the cladding layer.